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Human fibroblasts in culture, coloured scanning electron micrograph (SEM). A fibroblast is a cell common in the connective tissue that synthesizes and continuously secretes precursors of the extracellular matrix in mammal tissues. Like other cells of connective tissue fibroblasts are derived from primitive mesenchyme. Their stem cell line produces the osteoblasts of bone, the adipocytes of fat, and the chondrocytes in cartilage. Fibroblasts provide a structural framework for many tissues and play a critical role in wound healing. Unlike epithelial cells fibroblasts do not form monolayers and can also migrate slowly over substratum as individual cells. Fibroblasts make collagens, glycosaminoglycans, reticular and elastic fibres, and glycoproteins found in the extracellular matrix. Fibroblasts are also grown as 'feeder cells' to help support the growth of stem cells. Magnification: x400 when shortest axis printed at 25 millimetres.